A study published in the Lancet which studied neutralising antibody responses and duration of immunity in people who were infected with COVID-19 found that different people had varying levels of antibodies.
Titled 'Dynamics of SARS-CoV-2 neutralising antibody responses and duration of immunity: a longitudinal study' published on March 23, the study monitored neutralising antibodies in patients who had recovered from COVID-19 up to 6 months Explaining the study, Dr Ravindra Mehta, senior consultant and HOD, Pulmonology and Interventional Pulmonology, Apollo Speciality Hospitals said that while in some, the antibody levels dropped fast, in other cases it persisted.
In some patients, it fluctuated and in others, the antibodies were present up to 6 months. The persistence of neutralising antibodies was associated with disease severity and sustained level of pro-inflammatory cytokines, chemokines, and growth factor, an excerpt of the study stated,
"This means those who had a severe infection, with inflammation caused by cytokine storm, were found to have antibodies up to 6 months. In those, where the infection was milder and they were asymptomatic, the antibody levels were low. However, T cell immunity, which is longer memory cells, were present in people, despite neutralising antibodies going away," Dr Mehta explained.
The rate of antibody levels waning suggests reinfection during the second and later waves of infection is likely to occur, limiting the viability of a herd immunity strategy before an effective vaccine, the study stated. Herd immunity depends on the availability of antibodies in a community but any antibodies reduce over a period of time.
If the infection is rapid, often the T-cells are not able to remember the antibody response as the B-cells, which are the neutralising antibodies, take over to fight the present infection, said Dr Sheela Chakravarthy, Director, internal medicine, Fortis Hospitals.
"As we do not know the response of memory T-cells, it is better to get vaccinated against COVID to stimulate them. They will thereby produce neutralising antibodies and booster doses can be given to prevent reinfection," Dr Sheela added.
The study also revealed that patients with persistent antibodies were older and had more comorbidities, including hypertension and diabetes mellitus.